Feast of souls - Celia Friedman

In the High Kingdom of Danton Aurelius, magisters from across the known world are gathering for an unusual meeting. The High King's son is dying of an apparently incurable wasting disease, and he has charged them with providing an explanation and a cure. There is a mystery here, but not the one the High King thinks: the magisters know the cause of the prince's illness but they dare not reveal it for fear that it will expose the secret at the heart of their order. No, the mystery is not what is responsible, but who. . .

Now the magisters must embark upon a manhunt, racing against time, before the High King learns the truth. But they have not counted on the young prince's determination to control his own fate, nor on the existence of Kamala, a young woman schooled in their own arts, who will soon shake the world to its very roots.